Catalyzed shock tube reactions



March 15, 1966 LA ER 3,240,689

CATALYZED SHOCK TUBE REACTIONS Filed July 10, 1962 |NVENTOR= JAMES L. LAUER AZ HZW ATTORNEY existing devices of variable design.

'and US. 2,986,506. magnetically driven shock waves are created by exposing United States Patent 3,240,689 CATALYZED SHOCK TUBE REAiITIONS James L. Lauer, Penn Wynne, Pa., assignor to Sun Gil Company, Philadelphia, Pa., a corporation of New Jersey Filed July 10, 1962, Ser. No. 208,699 12 Claims. (Cl. 204-156) This invention relates to a method of increasing the yield of unsaturates produced during the shock wave induced pyrolyses of gaseous alkanes.

More particularly, this invention concerns the use of hydrogen halide and halohydrocarbon catalysts to increase the quantities of aromatic and unsaturated hydrocarbons produced during shock tube pyrolysis of alkanes and cycloalkanes having 2-5 carbon atoms, as compared to amounts of these unsaturates produced under the same reaction conditions in the absence of catalyst.

The term shock wave pyrolysis refers to those reactions wherein the energy source utilized to initiate the reaction is a shock wave or shock impulse derived from electrical, magnetic, or mechanical means.

The term shock tube refers to a reaction chamber of variable design used to contain the reactant or reactants exposed to the transforming shock waves. The term shock tube includes stationary as well as rotating shock tube devices, the latter rotating devices sometimes being referred to as continuous shock tube devices. An example of a continuous shock tube device is the socalled wave engine wherein the rotation of the shock tube components allow for a continuous pulsating type of operation. Wave engine shock tubes provide an effective means of scaling up processes found to be operable in conventional stationary shock tubes.

The shock waves used in the novel process of this invention can be derived from any number of presently These devices can utilize any convenient means for producing the variable shock impulses or waves including mechanical means, electrical means, magnetic means, sonic means, or any combination thereof. A common method of utilizing mechanical means is by having an inert gas (driver gas) such as helium or nitrogen under a pre-determined high pressure and separated by a rupturable disc or diaphragm from the reactant gases under low temperatures. When the disc is ruptured, the collision of the inert driver gas and reactants momentarily creates reaction conditions of extremely high temperature and pressure.

A shock tube found to be much more advantageous for the novel catalysis of this invention is a modification of the device described by Friel and Lauer in US. 2,986,505 In this device shown in FIGURE 1,

an inert driver gas or gas mixture to discontinuous spark discharges across a pair of electrodes of Which the ground electrode is connected to a lead parallel to the spark gap and closely spaced to it. The magnetic field of the lead is perpendicular to the discharged current so that when a spark discharge is struck between the electrodes, there is a force exerted across the spark discharge which appreciably increases the velocity of the shock wave generated by the heating effect of the spark. These shock waves rupture a thin diaphragm placed between the reactor con 3,240,689 Patented Mar. 15, 1966 tain-ing the process gas and the electrode pair. After rupturing the diaphragm, the shock waves pass through the process gas subjecting it to pulses of high temperature and pressure. The result of these high temperature and pres-sure pulses is to create pyrolysis conditions within the reactor almost instantaneously. Upon cessation of the electrical discharge, the process mixtures rapidly return to ambient temperatures and normal pressure and the reaction ceases.

The purpose of the aforementioned rupturable diaphragm is to confine the hydrocarbon-catalyst mixture to the reaction tube to await compression and pyrolysis by the shock wave. If the diaphragm is omitted from the apparatus, part of the hydrocarbon catalyst mixture which migrates to the electrodes will be reacted at the electrodes under much less severe reaction conditions than is desired. Thus the high energy needed to cause the desired reaction is diffused and the yields of the desired reaction products are adversely alfected.

The pyrolysis of the gaseous alkanes to higher value unsaturates and aromatics is potentially attractive for several reasons. These alkanes are readily available from petroleum distillates and natural gases and are inexpensive starting materials. Because of their relatively low molecular weights and molecular size, moderate energy shock waves (those which create reaction temperature of about 1000-2000 C.) bombard these molecules traveling at very high velocities within the shock tube and bring about the aforedescribed extreme reaction conditions of high temperatures and pressures for very short periods of time. Shock tube pyrolysis in general appears to offer substantial advantages for pyrolytic reactions as compared to conventional thermal pyrolysis. For example, the extremely high reaction temperatures and pressures that result from shock tube pyrolysis are reached almost instantaneously compared to conventional direct thermal pyrolysis processes. The return of the shock tube to ambient temperatures and pressures from the extreme reaction conditions is also very rapid. Because of the short lived periods of extreme temperatures and pressures in the reaction tube, comparatively unstable reactants can be used in shock tube pyrolysis Whereas in conventional thermal pyrolysis these more sensitive reactants would be destroyed or altered before the desired reaction could take place. Similarly, the shock tube pyrolytic process is conducive to the formation of heat and pressure sensitive products which are more prone to rearrange or be destroyed during the cooling down period after pyrolysis, when reaction temperatures and pressures in thermal processes are still considerable. Unfortunately, non-catalyzed shock tube pyrolysis processes have been relatively unsuccessful. Yields are low and varying reaction conditions and pressures have not made any substantial improvements in the process.

Unexpectedly, it has been found that the addition of small quantities of hydrogen halides or halohydrocarbons increases the yield of the unsaturated products and aromatics many fold, particularly ethylene, the acetylenes, and benzene. In addition to the hydrogen halides, halohydrocarbons such as chloroform, trichloroethane, ethylchloride and the like also exert this catalytic eifect. Hydrogen bromide and hydrogen chloride are particularly favored as the catalytic agent's because of their superior catalytic activity and lower cost, and hydrocarbons of from C -C are the preferred charges because of the much larger increases of aromatics observed throughout this hydrocarbon range. While the mechanism for this shock tube catalysis is presently unclear, the addition of catalytic quantities of the hydrogen halides or halohydrocarbons increases the yield of benzene and the unsaturates including ethylene and the acetylenes significantly. In some instances this increase in ethylene and acetylene production is as much as 5-8 times the yield obtained in non-catalyzed shock tube reaction.

The amount of catalyst necessary is variable and is dependent upon several factors such as the design of the shock tube used, the strength of the shock wave, operating temperatures, and pressures, the driver gas used, as well as the particular alkane reactant used. However, using the shock tube device illustrated in FIGURE 1, the operable range of catalyst is from 0.005 to 20 parts by weight of hydrogen halide to 100 parts of hydrocarbon reactant. The preferred range has been found to be from 0.01 to 2 parts by weight of the hydrogen halide to 100 parts of hydrocarbon. Conversion of the hydrocarboncatalyst mixture to the aromatic and unsaturated product is noticeable at 500750 C. and becomes substantial above 750 C.

In order to illustrate the novel catalysis of the alkanes in the preferred shock tube device, the following description of the operation of the preferred shock tube shown in the attached drawing is submitted:

A reaction tube 8 is provided with a valved line 9 leading to a suitable means for regulating the pressure in tube 8, such as a vacuum pump (not shown). Another valved line 11 regulates the pressure of the inert driver gas. A thin rupturable diaphragm is placed a convenient distance between the ends of the reaction tube 8. A pair of stainless steel electrodes 12 and 13 respectively, having a spark gap therebetween are located in tube 8 adjacent one end thereof. A second pair of electrodes 14 and 15 and a capacitor 16 are connected in series with electrodes 12 and 13, the breakdown voltage of the gap between electrodes 14 and 15 being higher than that of the gap between electrodes 12 and 13. Ground lead 17 which is connected to electrode 13 is formed of heavy brass strap, and passes upwardly in close juxtaposition to the gap between electrodes 12 and 13. A capacitor 16 is energized by a high voltage power supply 18.

In the operation of the preferred apparatus, the reactor 8 is filled with a mixture of the process gas (the hydrocarbon gas to be reacted), in this instance an alkane reactant, and the hydrogen halide catalyst. The pressure within the reactor 8 is adjusted to the desired value. The electrode (arc) portion of the tube is filled with an inert driver gas such as helium, argon, nitrogen, or the like. The pressures are preferably low, from about 2 mm. to about 60 mm. of mercury absolute, although atmospheric or higher pressures can be used.

The capacitor 16 is then charged by the power supply 18 to a voltage sufiicient to break down the gap between electrodes 14 and 15. Since the break-down voltage between electrodes 12 and 13 is less than that between electrodes 14 and 15, the spark will jump the gap between electrodes 12 and 13. When this happens, the inert driver gas between the electrodes is suddenly heated to a high temperature and a rapid expansion results. This rapid expansion generates a shock wave which ruptures the diaphragm 10 and propagates along the length of the reactor 8. Simultaneously, current flowing through the ground lead 17 sets up a magnetic field which exerts a force in the same direction as the shock wave travels. The combination of the electrical discharge and the magnetically driven shock wave serves to convert a far higher percentage of the hydrocarbon to unsaturates than when the electrical discharge alone is used, per given amount of energy input.

Similarly, the addition of the above-mentioned catalytic amount of hydrogen halide or halohydrocarbons to the hydrocarbon-catalyst mixture gives a substantial increase in yield of unsaturates and benzene produced as compared to the yields obtained in runs made on inert gashydrocarbons alone.

The data in the following table gives the amount of ethylene, acetylene, and benzene obtained using the abovedescribed shock wave pyrolyses with various hydrocarbons of the C C range with and without the hydrogen halide catalyst. In all the experimental results presented, an aluminum alloy was used as diaphragm, the inert driver gas was helium and an electrical discharge of 16 kv. was used.

Table Hydrocarbon Catalyst Percent Percent Percent Ethylene Acetylene Benzene Methane None 5.3 43.9 D0. 1.0% 5.1 40.3

I-lBr. Ethane None 2.7 5.2 5.0 0 1.0% 5.3 5.8 23.0

HBr. n-Propnne None 3.8 (I) HBr. n-Pentane None 0. 3 3. 7 4. 0 Do. 1.0% 2.6 9.4

HBr. n-Hexano i Nonei 0.8 5.1 24.8 D0 1.0% 0.8 5.8 24.0

HBr. Cyclohexane None... 1.7 11.6 41.0

HBr. l\lethylcyclopentane None 0.9 11.8 4n.0

HBr

1 None.

In all of the above runs the experimental conditions were substantially identical.

As can be seen from the data presented, the yields of one or more of the three listed unsaturated hydrocarbon products were increased when a catalytic quantity of HBr was present when the hydrocarbon charge was of the C C range. This was particularly so with respect to benzene production. However, with either higher or lower molecular weight hydrocarbons, such yield increase was not experienced.

Substantially analogous results are obtained when hydrogen chloride or halohydrocarbons are used as the catalyst in place of hydrogen bromide.

We claim:

1. A process for increasing the yield of olefinic and aromatic hydrocarbons obtained in the shock wave pyrolysis of hydrocarbons, comprising subjecting a reaction mixture comprising an alkane having from 2 to 5 carbon atoms and a catalytic amount of a halide selected from the group consisting of hydrogen halides and halohydrocarbons, to a series of shock waves of sufficient intensity to produce reaction temperatures of at least 800 C. V

2. The process of claim 1 wherein the hydrocarbon having from 2 to 5 carbon atoms is ethane, and the catalyst is hydrogen bromide.

3. The process of claim 1 wherein the hydrocarbon having from 2 to 5 carbon atoms is propane, and the hydrogen halide is hydrogen bromide.

4. The process of claim 1 wherein the hydrocarbon having from 2 to 5 carbon atoms is butane, and the hydrogen halide is hydrogen bromide.

5. The process of claim 1 wherein the hydrocarbon having from 2 to 5 carbon atoms is pentane, and the hydrogen halide is hydrogen bromide.

6. The process of claim 1 wherein the hydrogen halide is hydrogen chloride.

7. A process for increasing the yield of olefinic and aromatic hydrocarbons obtained in the shock tube pyrolysis of hydrocarbons, comprising subjecting a reaction mixture comprising an alkane having from 2 to 5 carbon atoms and a catalytic amount of a halide selected from Ihe group consisting of hydrogen halides and halohydrocarbons, to a substantially simultaneous series of discontinuous direct current spark discharges and magneticallydriven shock Waves of sufiicient intensity to produce reaction temperatures within the shock tube of at least 800 C.

8. The process of claim 7 wherein the hydrocarbon having from 2 to 5 carbon atoms is ethane, and the catalyst is hydrogen bromide.

9. The process of claim 7 wherein the hydrocarbon having from 2 to 5 carbon atoms is propane and the hydrogen halide is hydrogen bromide.

10. The process of claim 7 wherein the hydrocarbon having from 2 to 5 carbon atoms is butane and the hydrogen halide is hydrogen bromide.

6 11. The process of claim 7 wherein the hydrocarbon having from 2 to 5 carbon atoms is pentane and the hydrogen halide is hydrogen bromide.

12. The process of claim 7 wherein the hydrogen halide 5 is hydrogen chloride.

References Cited by the Examiner UNITED STATES PATENTS 5/1961 Lauer et. a1. 204156 3,027,414 3/1962 Fruhwirth 260679 JOHN H. MACK, Primary Examiner. 

1. A PROCESS FOR INCREASING THE YIELD OF OLEFINIC AND AROMATIC HYDOCARBONS OBTAINED IN THE SHOCK WAVE PYROLYSIS OF HYDROCARBONS, COMPRISING SUBJECTING A REACTION MIXTURE COMPRISING AN ALKANE HAVING FROM 2 TO 5 CARBON ATOMS AND A CATALYTIC AMOUNT OF A HALIDE SELECTED FROM THE GROUP CONSISTING OF HYDROGEN HALIDES AND HALOHYDROCARBONS, TO A SERIES OF SHOCK WAVES OF SUFFICIENT INTENSITY TO PRODUCE REACTION TEMPERATURE OF AT LEAST 800*C. 